This invention relates to a method for mounting clip type circuit elements on a printed circuit board and an apparatus for performing the same.
More particularly, this invention relates to an improvement in the method and apparatus for mounting chip type elements on a printed circuit board, as disclosed in the specification of U.S. Pat. No. 4,127,432, in which the chip type circuit elements are mounted on a printed circuit board at predetermined positions by pushing up each circuit element stack inserted in a magazine which is vertically held and is inserted through a corresponding step-hole defined by a lattice-shaped and horizontally placed magazine guide.
The method disclosed in the specification of U.S. Pat. No. 4,127,432 is advantageous over the conventional method of using an NC (numerical control) apparatus in that chip type circuit elements can be mounted on a printed circuit board at a higher speed by using inexpensive and simple apparatus. An electronic circuit assembled according to this method, however, is susceptible to such serious defects as imprecise positioning of the chip type circuit elements on the printed circuit board during attachment, occurrence of open or high resistance points in the circuit due to improper mounting and resulting substantial decreases in the yield of the product.
These defects involved in the technique disclosed in the specification of U.S. Pat. No. 4,127,432 are due to the following structural features:
(1) Chip type circuit elements stacked in hollow tubular magazines are directly pressed against an adhesively treated printed circuit board by several dozens of respective thrust pins to mount the elements on the printed circuit board.
(2) In order to mount the chip type circuit elements, which are stacked in hollow tubular magazines, on the printed circuit board, the printed circuit board, inorder to confront said magazines, is arranged so that the surface against which the connectors for the circuit elements abut is directed downwardly.
In connection with the defect-causing structural feature (1), it is very difficult to press chip type circuit elements stacked in different heights in the respective magazines onto the adhesive layer formed on the printed circuit board under a uniform pressure by several dozens of the thrust pins. Although a compression spring is provided to adjust the pressing force of the thrust pins, the fatigue of the compression sprin is extreme at a high speed operation and the printed board is likely to lose its flatness and become warped. If such printed circuit boards are employed, it is very difficult to maintain a predetermined space between the top ends of the magazines, that is, the top ends of the thrust pins, and the mounting surface of each printed circuit board. Moreover, the adhesive applied to the printed circuit board is likely to adhere to the top ends of the thrust pins, resulting in occurrence of serious problems.
When the structural feature (2) is adopted, the adhesive layer is naturally formed on the bottom major surface of the printed circuit board until they are introduced into a subsequent soldering step. As a result, change of position or separation of the elements frequently occurs. More specifically, the printed circuit board having the circuit elements temporarily supported on the bottom surface thereof by means of the adhesive is delivered by belt means and the adhesive, which is thermosetting, is cured to fix the circuit elements to the printed circuit board. For effecting curing of the adhesive, the printed circuit board is inverted. During the delivering and inversion steps, the circuit elements temporarily held to the bottom surface of the printed circuit board are likely to deviate from their predetermined positions or separate from the printed circuit board.